1. Field of the Invention
This disclosure relates to the field of treatment processes for wooden articles, specifically to a tank and system for treating railroad crossties with a thickened borate solution.
2. Description of Related Art
While the vast majority of people are far more familiar with roadways and trucking as part of the transportation infrastructure, there can be no doubt that the railroad is still far from obsolete and in many parts of the world is still a primary form of transportation. While many trains today are small passenger (or light rail) trains that serve cities and provide public transportation, in many respects passenger transportation is a very small percentage of rail transportation. A huge amount of goods still travel by rail. These freight lines (or heavy rail) tracks and trains are still an essential component of the world economy.
Currently, the United States has more than 220,000 miles of railroad track suitable for freight transport and many countries also include a large amount of similar railway. While light rail tracks are typically mounted in concrete to provide for a smoother ride, large freight rail lines, which handle significantly greater load, still utilize traditional wooden crossties (or “sleepers”) to support the rails.
The number of wooden crossties in use in the United States, and throughout the world, to support these railways is huge. Every mile of track in the United States has around 3,000 crossties holding it together. Thus, simple maintenance of existing lines, assuming a crosstie can have an operational life of 30 years, creates a need for over 20 million crossties every year.
While wood has a number of beneficial properties for use as crossties including its renewable nature and high load bearing capability (while still being flexible), it has one inherent weakness which is its increased vulnerability to degradation over time compared to alternative materials. In order to help preserve wood crossties (and provide them with the upwards of 30 year useful life which is generally standard) the wooden crossties have for many years been treated with chemicals to inhibit rotting and attacks from wood-eating insects. For the vast part of history, this treatments is with coal-tar creosote.
The processes for treating crossties with creosote are well established and generally involve placing dried crossties in a sealed chamber and exposing them to increased pressure while creosote is introduced in order to force the creosote into the wood cells to provide sufficient saturation. This process is relatively slow, as only a relatively small number of crossties can be simultaneously treated and they often require specific positioning, and is also relatively difficult because of the pressurization requirements. Further, long drying periods of the crossties which are necessary prior to treatment can result in incipient decay prior to treatment and further complicate the process.
Creosote is also a generally unpopular material. It has been labeled as a carcinogen and is generally regarded as toxic by a number of regulatory agencies. Further, over time, it can leach from crossties into soil and related environments which has resulted in environmental concerns from crosstie waste and on railway beds. Further, used crossties, which were a popular building material for retaining walls or similar structures, are growing less popular due to these concerns meaning that more crossties need to be disposed of in landfills or other holding facilities.
It has been proposed that crossties be treated with a borate solution as borates are generally less toxic and easier to handle. Borate treatment, however, has thus far followed the same general treatment patterns as creosote treatment. Crossties are allowed to dry and are then treated under pressure and elevated temperature to insure proper saturation. While some non-pressurized methodologies utilizing higher concentrate “dips” have been proposed, there have been no solutions proposed for how to integrate such treatments into the crosstie manufacturing process.